Effect of Additional Transmitting Coils on Transfer Distance in Multiple-Transmitter Wireless Power Transfer System

Wireless power transfer (WPT) technology has been widely introduced and developed over the past few years. Nevertheless, the basic WPT configuration using one transmitting (Tx) coil and one receiving (Rx) coil still achieves very limited performance in terms of power transfer distance. To overcome this limitation, various multi-coil WPT systems using three or more coils have been studied. Among them, a multiple-input single-output (MISO) structure can provide the Rx with advanced freedom in an extensive lateral area. However, few studies have investigated how far multi-Tx coils can increase the transfer distance. In this paper, we analyze the transfer distance and lateral coverage based on the generalized critical coupling condition and system energy efficiency according to the number of additional Tx coils in the MISO WPT system. The results demonstrate that the MISO WPT system using planarly arranged Tx coils improves by barely 1% in the optimal transfer distance, which achieves the maximum output power condition in a single-Tx WPT system. To validate our analysis, the MISO WPT system with seven Tx coils and seven LCC inverters was implemented and its performance was assessed. The measured results agreed well with the theoretically calculated results.